256 SCIENCE PROGRESS 



the Glass from one end to the other." Also it seems that 

 he did not work so often with the slit and lens arrangement 

 for producing spectra as with the pinhole or ordinary camera 

 methods ; the motion of the sun in the sky would cause less 

 trouble with the two latter arrangements. Besides, the years 

 1665-6 were a time of such great mental activity on the part 

 of Newton — they saw the discovery of the binomial theorem, 

 differential and integral calculus, to say nothing of the work 

 on gravitation — that he must have experimented at high 

 speed. So he missed the lines, and it was reserved for Fraun- 

 hofer to discover them 150 years later. 1 



In addition to the sun, we know from p. 26 of the Lectiones 

 Opticce, published in Latin after his death, but not from his 

 Opticks, that Newton examined also the spectrum of Venus, 

 using the " ordinary camera " method. He says that the 

 spectrum was not very bright but still easily visible, comments 

 on its extreme narrowness, and states that he believes it would 

 be possible to observe the spectra of the stars of the first magni- 

 tude, especially Sirius, in the same way. From a subsequent 

 page we infer that this experiment had been successfully tried. 



So much for Newton's experimental arrangements. We 

 come now to discuss his nomenclature for the colours of the 

 spectrum. 



When first he describes the spectrum (pp. 22 and 23 of the 

 Opticks) there are only five colours mentioned, namely, red, 

 yellow, green, " blew," violet, and again on p. 87 he refers to 

 the spectrum as showing the usual colours on a piece of paper, 

 namely, red, yellow, green, blue, violet ; blue this time is spelt 

 in the modern way. This, I think, is the natural description 

 to be expected from a man with normal colour vision who sees 

 a bright spectrum spread out as a whole before him for the 

 first time ; only when the spectrum is examined strip by strip, 



1 The question as to why Newton missed the Fraunhofer lines has been con- 

 sidered by G. Griffith {Brit. Ass. Rep. 1885, p. 941) and by Alexander Johnson 

 {Trans. Roy. Soc. Canada, 9, p. 49, 1891 ). Both authors point out that it was 

 not due to his using a circular aperture instead of a slit, and that the textbooks 

 are wrong on this point. Griffith states that the arrangement was good enough to 

 show the lines, but that possibly part of the work was left to an assistant, and that 

 the latter missed them. Johnson repeated Newton's experiment under similar 

 conditions, and saw plainly ten Fraunhofer lines when the slit was ^ in. wide (the 

 greatest width mentioned by Newton). Newton's arrangement of a circular hole 

 iV in. in diameter was found by Johnson to show four lines very distinctly. 



